LMS vs XMSS: Comparison of Stateful Hash-Based Signature Schemes on ARM Cortex-M4

Stateful hash-based signature schemes are among the most efficient approaches for post-quantum signature schemes. Although not suitable for general use, they may be suitable for some use cases on constrained devices. LMS and XMSS are hash-based signature schemes that are conjectured to be quantum secure. In this work, we compared multiple instantiations of both schemes on an ARM Cortex-M4. More precisely, we compared performance, stack consumption, and other figures for key generation, signing and verifying. To achieve this, we evaluated LMS and XMSS using optimised implementations of SHA256, SHAKE256, Gimli-Hash, and different variants of KECCAK. Furthermore, we present slightly optimised implementations of XMSS achieving speedups of up to 3.11x for key generation, 3.11x for signing, and 4.32x for verifying.